The present application relates to printing systems and, more particularly, to printing systems for printing cards that incorporate photosensitive microcapsules.
A common method of fabricating printed identification cards uses dye diffusion thermal transfer, or D2T2, to transfer colored dyes from a print ribbon to the blank identification card. In this process, a ribbon carrying dye in a polymeric binder is heated from behind with a thermal print head (TPH), while in contact with a vinyl, or PVC, surface. As each pixel heats the ribbon, the dye melts and diffuses from the ribbon, into the vinyl surface. Printing with successive yellow, magenta, and cyan panels across the substrate, creates a three-color image in the surface. Since the amount of transferred dye is directly proportional to the amount of heat from the corresponding pixel, true color representation is possible in the printed image. However, when using D2T2 methods to print to hard, plastic identification cards, the apparent quality of the printed image frequently depends on the ability of the mechanical printer systems to accurately register each of the printing sequences, yellow, magenta, cyan, and black, and to smoothly move the substrate and ribbon beneath the TPH during the print sequences. Furthermore, since the efficiency of transferring the dye from the heated pixel to the surface of the card depends on close, intimate contact, the presence of dirt, debris, or surface imperfections will preclude contact of the ribbon with the surface, leaving corresponding voids and vacancies in the printed image.
Frequently, the D2T2 print ribbon also contains a resin panel to print black resin for barcode applications and a clear protective overlaminate panel for application over the printed image. Mass transfer of both the resin and the overlaminate panels is accomplished as the TPH heats the ribbon and the material is released from the ribbon, and adheres to the surface of the card. Again, the apparent quality of the printed resin image, and the coherence of the overlaminate panel depends on the ability of the mechanical printer system to accurately register each of the ribbon panels, and smoothly move the card, and the ribbon beneath the TPH during the print sequences. However, while imperfections in surface smoothness interfere with dye transfer, it is surface contamination, such as oils, that interfere with the adhesion of the resin and overlaminate to the surface of the card.
Recent innovations to reduce the effect of the card surface in identification card printing include D2T2 printing to an Intermediate Transfer Media, InTM, which is transferred to the card surface and ink jet printing to a receptive card surface. While these techniques can reduce the dependence of the perceived quality of the printed data on the quality of the surface characteristics of the card, transferring the colorant from a reservoir to the surface remains the printing mechanism. As such, printing speed is fundamentally inversely related to the quality of the printed data; i.e., the more photo realistic images are achieved by slowing down the print speed and, conversely, printing identification cards quickly generally provides very non-photo realistic images.
Thus, an improved method of generating photo realistic identification cards quickly presumes that the colorants, or colorant precursors, are already present in the card. Saigo, et al., U.S. Pat. No. 6,229,558 teaches such a printer and printing method. The printer includes a carriage for scanning red, green, and blue light over print paper containing photosensitive microcapsules encapsulating a color developing material and a photo curing material and having an image receiving layer for developing color by a reaction of the color developing material with the image receiving layer. However, the light is applied with a scanning mechanism, fundamentally repeating the inverse relationship of ink-jet printingxe2x80x94print speed is increased by reducing the resolution of the printing and resolution of the printed image is increased by reducing the scanning speed. Also, since the mechanical pressure is applied to the mediaxe2x80x94a process called developingxe2x80x94by a scanning ball mechanism, the same inverse relations exists, where a higher resolution of the development results in a longer development time.
The present invention addresses the limitations of the above-described prior art. The card printing system of the present invention includes a cartridge sub-assembly and a printer sub-assembly. The cartridge sub-assembly encloses a stack of horizontally positioned cards that have each been plied with photosensitive microcapsules. The printer sub-assembly interfaced with the cartridge sub-assembly to obtain a card from the stack. The printer sub-assembly then forms a latent image upon the photosensitive microcapsules upon the obtained card and develops that image by applying a mechanical pressure to the photosensitive microcapsules with a developer array. The develop array is a block containing a number spring-loaded developer balls.
A method of the present invention includes the following steps: (1) supplying an identification card that has been previously plied with photosensitive microcapsules; (2) forming a latent image upon said identification card; and (3) developing the latent image by application of an array of pressure points to the latent image.